Apparatus and methods for selectively etching silicon oxide films

ABSTRACT

An apparatus and methods for selectively etching a particular layer are disclosed. The apparatus and methods are directed towards maintaining the etch rate of the particular layer, while keeping intact a non-etched layer. A gas mixture may be flowed onto the substrate in separate loops having an oxide layer and an oxynitride layer as an etch layer and a nitride layer as a non-etched layer, for example. A reaction between the resulting gas mixture and the particular layer takes place, resulting in etching of the oxide layer and the oxynitride layer while maintaining the nitride layer in the above example.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Non-provisional of, and claims priority to and the benefit of, U.S. Provisional Patent Application No. 63/007,276, filed Apr. 8, 2020 and entitled “APPARATUS AND METHODS FOR SELECTIVELY ETCHING SILICON OXIDE FILMS,” which is hereby incorporated by reference herein.

FIELD OF INVENTION

The present disclosure generally relates to an apparatus for processing semiconductor wafers. More particularly, the disclosure relates to an apparatus and methods for selectively etching a particular film (such as silicon oxide) on a semiconductor wafer while keeping another film intact.

BACKGROUND OF THE DISCLOSURE

During formation of semiconductor devices, there is a significant likelihood that multiple films would be formed. For example, there may be both silicon nitride films and silicon oxide films deposited on a patterned wafer.

Certain applications may require that the processed patterned wafer have a particular film on it, such as silicon nitride, while removing another film. These may include logic and memory applications. In these cases, failing to remove one film, such as silicon oxide, may result in malfunctioning of the devices. In addition, processes to remove a silicon oxide film may result in thinning, damage, or removal of the silicon nitride film, reducing the ability of the device to store charges, which may prove to be critical for performance in memory applications for example.

As a result, an apparatus and methods that exhibit selectivity for etching one particular film over another are desired.

SUMMARY OF THE DISCLOSURE

In accordance with at least one embodiment of the invention, a method for selectively etching a film (e.g., a film used in the formation of semiconductor devices) deposited on a substrate is disclosed. The method comprises: providing a substrate in a reaction chamber of a semiconductor processing device, wherein the substrate has an oxide layer, a nitride layer, and an oxynitride layer; performing a first etching process, wherein the first etching process comprises flowing a hydrogen precursor gas, a fluorine precursor gas, and an inert gas onto the substrate; performing a second etching process, wherein the second etching process comprises flowing a hydrogen precursor gas, a fluorine precursor gas, and an inert gas onto the substrate; wherein the first etching process is repeated a predetermined number of times and the first etching process removes the oxynitride layer from the substrate and keeps the nitride layer substantially intact; and wherein the second etching process is repeated a predetermined number of times and the second etching process removes the oxide layer from the substrate and keeps the nitride layer substantially intact.

In accordance with at least one embodiment of the invention, a system for selectively etching a film disposed on a substrate is disclosed. The system comprises: a reaction chamber configured to hold and process a substrate, wherein the substrate has an oxide layer, a nitride layer, and an oxynitride layer; a fluorine precursor source configured to provide a fluorine precursor gas, the fluorine precursor gas comprising at least one of: nitrogen trifluoride (NF₃); carbon tetrafluoride (CF₄); sulfur hexafluoride (SF₆); hydrogen fluoride (HF); hydrofluoric acid (HF) with water vapor; or fluorine (F₂); a hydrogen precursor source configured to provide a hydrogen precursor gas, the hydrogen precursor gas comprising at least one of: ammonia (NH₃); hydrazine (N₂H₄); urea (NH₂CONH₂); or hydrogen (H₂); and an inert gas source configured to provide an inert gas, wherein the inert gas comprises at least one of: argon; krypton; helium; xenon; or nitrogen; wherein a gaseous mixture of the fluorine precursor gas, the hydrogen precursor gas, and the inert gas is flowed onto the substrate, resulting in an etching of the oxide layer and the oxynitride layer while maintaining intact the nitride layer in an etching process.

This summary is provided to introduce a selection of concepts in a simplified form. These concepts are described in further detail in the detailed description of example embodiments of the disclosure below. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

These and other features, aspects, and advantages of the invention disclosed herein are described below with reference to the drawings of certain embodiments, which are intended to illustrate and not to limit the invention.

FIGS. 1A-1D are cross-sectional illustrations of a semiconductor device in accordance with at least one embodiment of the invention.

FIG. 2 is a flowchart of a method for selectively etching a film in accordance with at least one embodiment of the invention.

FIG. 3 is a schematic illustration of a semiconductor processing system in accordance with at least one embodiment of the invention.

FIG. 4 is a schematic illustration of a semiconductor processing system in accordance with at least one embodiment of the invention.

It will be appreciated that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help improve understanding of illustrated embodiments of the present disclosure.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Although certain embodiments and examples are disclosed below, it will be understood by those in the art that the invention extends beyond the specifically disclosed embodiments and/or uses of the invention and obvious modifications and equivalents thereof. Thus, it is intended that the scope of the invention disclosed should not be limited by the particular disclosed embodiments described below.

The illustrations presented herein are not meant to be actual views of any particular material, structure, or device, but are merely idealized representations that are used to describe embodiments of the disclosure.

Various embodiments are related to a cleaning process for removing a silicon oxide, a germanium oxide, or a metal oxide material from an exposed surface of a substrate. The embodiments may also be used to remove at least one of: silicon; metals in its elemental form; alloys of various metals; oxides related to the alloys of various metals; silicon; or germanium. It may be understood that a resulting cleaned surface will allow for formation of high quality semiconductor layers, such as epitaxially grown silicon, for example.

FIG. 1A illustrates a semiconductor device 100 prior to undergoing a cleaning process. The semiconductor device 100 comprises a substrate 110; an intermediate layer 120; a nitride layer 130; and an oxide layer 140. The substrate 110 may comprise at least one of: silicon or silicon germanium. The intermediate layer 120 may comprise a dielectric layer, such as silicon nitride, silicon carbonitride, or silicon boronitride, for example. The intermediate layer 120 may comprise other materials as well, such as silicon carbide or silicon oxycarbide, for example. The nitride layer 130 may comprise silicon nitride or a metal nitride, such as aluminum nitride. The oxide layer 140 may comprise at least one of: silicon oxide; germanium oxide; aluminum oxide; cobalt oxide; or tungsten oxide, for example.

Formation of the layers may take place via epitaxial deposition, chemical vapor deposition (CVD), atomic layer deposition (ALD), plasma enhanced atomic layer deposition (PEALD), or plasma enhanced chemical vapor deposition (PECVD), for example. It is desired that a cleaning process be able to entirely remove or remove a targeted thickness of the oxide layer 140, but keep the nitride layer 130, the intermediate layer 120, and the substrate 110 intact. Such a result is shown in FIG. 1D.

FIG. 1B illustrates the semiconductor device 100 after a period of time within a reaction chamber. The period of time may be between an initial deposition of the nitride layer 130 and an etching step of the oxide layer 140. This period of time may be unavoidable due to the complexities involved with manufacturing integrated circuits. During that period of time, the semiconductor device 100 is exposed to the ambient environment of the reaction chamber.

Exposure of the semiconductor device 100 to the ambient environment causes oxidation of the nitride layer 130, resulting in the formation of an oxynitride layer 150. The longer the oxidation occurs, the thicker the oxynitride layer 150 may become. The oxynitride layer 150 causes a greater loss of the nitride layer 130, in comparison to a nitride layer that remains unoxidized.

Protection of the nitride layer 130 is desirable as the nitride layer 130 may be a crucial part of an integrated circuit, or it may be a mask layer to protect another layer on the patterned substrate. Presence of the oxynitride layer 150 may prove to be problematic as removal of the oxynitride layer 150 is a self-catalyzed reaction facilitated by the byproduct water (H₂O) molecules formed on the surface of the substrate. The existence of these water molecules may lead to undesired etching of the nitride layer 130 if the etching is not stopped after the oxynitride layer 150 is removed. As a result, the etching step of the oxynitride layer 150 may be stopped and a bake step may be employed to remove the byproduct water (H₂O) molecules in order to preserve the nitride layer 130.

FIG. 1C illustrates the semiconductor device 100 after a first etch process loop takes place. The first etch process loop ideally removes an entire portion of the oxynitride layer 150 and a portion of the oxide layer 140. It may turn out that a portion of the nitride layer 130 is also removed, but it is desired that removal of the nitride layer 130 is limited.

FIG. 1D illustrates the semiconductor device 100 after a second etch process loop takes place. The second etch process loop ideally removes the remainder of the oxide layer 140. Again, it may also turn out that a portion of the nitride layer 130 is removed, but is desired that removal of the nitride layer 130 is limited.

FIG. 2 illustrates an etching process 200 that may comprise: (1) a step for providing a substrate in a reaction chamber 210; (2) a step for a first etch process 220; (3) a step for an optional mild bake 230; (4) a step for a second etch process 250; (5) a step for an optional mild bake 260; and (6) a step for performing additional processing on the substrate 280.

The first etch process 220 and the optional mild bake 230 may be done again through a first etch process repeat step 240. The first etch process 220, the optional mild bake 230, and the first etch process repeat step 240 together comprise a first etch process loop. The first etch process repeat step 240 may be done more than once. Similarly, the second etch process 250 and the optional mild bake 260 may be done again through a second etch process repeat step 270. The second etch process 250, the optional mild bake 260, and the second etch process repeat step 270 together comprise a second etch process loop. The second etch process repeat step 270 may also be done more than once.

The step 210 may be done in a reaction chamber for performing epitaxial deposition, chemical vapor deposition (CVD), atomic layer deposition (ALD), plasma enhanced atomic layer deposition (PEALD), or plasma enhanced chemical vapor deposition (PECVD). The step 210 may also take place in a vertical furnace. A deposition step may take place after the substrate arrives into the reaction chamber and before the first etch process 220, resulting in a film deposited on the substrate. For example, the deposition step may result in the formation of the nitride layer 130 or the oxide layer 140 on the substrate.

Directed to removing the oxide layer 140 and the oxynitride layer 150, the first etch process 220 may comprise flowing a combination of gases into the reaction chamber. The combination of gases may include a fluorine gas, a hydrogen gas, and an inert gas. The combination of gases may include activated or radical versions of the gases listed above. The fluorine gas may comprise at least one of: nitrogen trifluoride (NF₃); carbon tetrafluoride (CF₄); sulfur hexafluoride (SF₆); hydrogen fluoride (HF); hydrofluoric acid (HF) with water vapor; or fluorine (F₂). The inert gas may comprise at least one of: argon (Ar); krypton (Kr); helium (He); xenon (Xe); or nitrogen (N₂). The hydrogen gas may comprise at least one of: ammonia (NH₃); hydrazine (N₂H₄); urea (NH₂CONH₂); hydrogen (H₂); an alcohol, such as methanol, ethanol, propanol, or isopropanol; an acidic gas, such as formic acid (HCOOH), acetic acid (CH₃COOH), or an acidic anhydride; or a mixture of the above.

In one embodiment of the invention, the fluorine gas and the inert gas may be activated by a remote plasma unit (RPU) prior to being combined with the hydrogen gas. In another embodiment of the invention, the fluorine gas, the inert gas, and the hydrogen gas may be combined in a gas manifold prior to being flowed into the reaction chamber.

The first etch process 220 may have settings that facilitate removal of the oxynitride layer 150. For example, the reaction chamber may be set to a temperature ranging between −20° C. and 150° C., between 0° C. and 100° C., or between 5° C. and 65° C. The duration of the first etch process 220 may be between 1 and 30 seconds, between 3 and 20 seconds, or between 3 and 10 seconds. The pressure of the reaction chamber during the first etch process 220 may be between 0.1 and 600 Torr, between 0.5 and 50 Torr, or between 0.5 and 4 Torr.

The mild bake step (optional) 230 may be employed after the first etch process 220. The first etch process 220 may result in formation of reaction byproducts that require removal. For example, during the first etch process 220, water (H₂O) molecules may be formed on the surface of the substrate. The mild bake step 230 would remove the H₂O molecules that could potentially interfere with subsequent processing steps.

During the mild bake step 230, a flow of inert gas into the reaction chamber may take place. The inert gas may comprise at least one of: argon (Ar); krypton (Kr); helium (He); xenon (Xe); or nitrogen (N₂). In addition, the reaction chamber may be set to a temperature ranging between 50° C. and 400° C., between 75° C. and 300° C., or between 90° C. and 250° C. The duration of the mild bake step 230 may be between 5 and 120 seconds, between 10 and 60 seconds, or between 10 and 30 seconds.

Directed to removing the oxide layer 140 and keeping the nitride layer 130 intact, the second etch process 250 may comprise flowing a combination of gases into the reaction chamber. The combination of gases may include a fluorine gas, a hydrogen gas, and an inert gas. The combination of gases may include activated or radical versions of the gases listed above. The fluorine gas may comprise at least one of: nitrogen trifluoride (NF₃); carbon tetrafluoride (CF₄); sulfur hexafluoride (SF₆); hydrogen fluoride (HF); hydrofluoric acid (HF) with water vapor; or fluorine (F₂). The inert gas may comprise at least one of: argon (Ar); krypton (Kr); helium (He); xenon (Xe); or nitrogen (N₂). The hydrogen gas may comprise at least one of: ammonia (NH₃); hydrazine (N₂H₄); urea (NH₂CONH₂); hydrogen (H₂); an alcohol, such as methanol, ethanol, propanol, or isopropanol; an acidic gas, such as formic acid (HCOOH), acetic acid (CH₃COOH), or an acidic anhydride; or a mixture of the above.

In one embodiment of the invention, the fluorine gas and the inert gas may be activated by a remote plasma unit (RPU) prior to being combined with the hydrogen gas. In another embodiment of the invention, the fluorine gas, the inert gas, and the hydrogen gas may be combined in a gas manifold prior to being flowed into the reaction chamber.

The second etch process 250 may have settings that facilitate removal of the oxide layer 140. For example, the reaction chamber may be set to a temperature ranging between −20° C. and 150° C., between 0° C. and 100° C., or between 5° C. and 65° C. The duration of the second etch process 250 may be between 5 and 120 seconds, between 5 and 60 seconds, or between 5 and 30 seconds. The duration of the second etch process 250 may be longer than that of the first etch process 220 in order to result in a greater etch rate of the desired film (in this case, the oxide film 140). The pressure of the reaction chamber during the second etch process 250 may be between 0.1 and 600 Torr, between 0.5 and 50 Torr, or between 0.5 and 4 Torr.

The mild bake step (optional) 260 may be employed after the second etch process 250. The second etch process 250 may result in formation of reaction byproducts that require removal. It is not expected during the second etch process 250 that water (H₂O) molecules may be formed on the surface of the substrate; however, other byproducts may be formed, such as non-catalyzing reaction byproducts. The mild bake step 260 would remove these byproducts (as well as any water molecules that may exist) that could potentially interfere with subsequent processing steps.

During the mild bake step 260, a flow of inert gas into the reaction chamber may take place. The inert gas may comprise at least one of: argon (Ar); krypton (Kr); helium (He); xenon (Xe); or nitrogen (N₂). In addition, the reaction chamber may be set to a temperature ranging between 50° C. and 400° C., between 75° C. and 300° C., or between 90° C. and 250° C. The duration of the mild bake step 260 may be between 5 and 120 seconds, between 10 and 60 seconds, or between 10 and 30 seconds.

The first etch process repeat step 240 may be repeated a different number of times in comparison to the second etch process repeat step 270. Such may be as a result of a different thickness of the oxynitride layer 150 and the oxide layer 140 needing to be removed from the substrate. By separating the first etch process repeat step 240 from the second etch process repeat step 270, a greater selectivity of etching the oxide layer 140 over the nitride layer 130 may be achieved. For example, an etching process in accordance with at least one embodiment of the invention may achieve an etching ratio (etching oxide layer:etching nitride layer) greater than 8:1, greater than 16:1, or greater than 40:1.

In accordance with another embodiment of the invention, selectivity of the etching process may be defined in a way that minimizes removal of the nitride layer 130 when a certain thickness of the oxide layer 140 is required to be removed by a specific application. The etching process in accordance with this invention may reduce an amount of loss in the nitride layer 130 with respect to the entire oxynitride layer 150 and the nitride layer by a percentage greater than 20%, greater than 50%, or greater than 80%.

After the second etch process repeat step 270 is complete, the substrate may undergo other processing in a step for performing additional processing 280. The additional processing step 280 may comprise deposition processes such as epitaxial deposition, chemical vapor deposition (CVD), atomic layer deposition (ALD), plasma enhanced atomic layer deposition (PEALD), or plasma enhanced chemical vapor deposition (PECVD), for example. Alternatively, the additional processing step 280 may comprise different etch processes to potentially remove a different material; for example, the different etch process may be used to remove a carbon-containing layer.

In accordance with at least one embodiment of the invention, a substrate processing system 300 is disclosed in FIG. 3. The substrate processing system 300 comprises: a reaction chamber 310; a remote plasma unit 320; a fluorine precursor source 330A; an inert gas source 330B; a hydrogen precursor source 330C; a pathway 340 disposed between the remote plasma unit 320 and the reaction chamber 310; and a plurality of gas lines 350A-350C linking the gas sources 330A-330C with the remote plasma unit 320 and the pathway 340.

The reaction chamber 310 comprises a substrate holder 310A configured to hold a substrate to be processed; and a showerhead 310B for distributing the gas onto the substrate. The substrate holder 310A may have an ability to control its temperature among different parts of the substrate holder 310A. The fluorine precursor source 330A and the inert gas source 330B provide gases that are activated by the remote plasma unit 320. The remote plasma unit 320 may comprise one created by MKS Instruments, Inc. or by Advanced Energy Industries, Inc.

In accordance with at least one embodiment of the invention, a substrate processing system 400 is disclosed in FIG. 4. The substrate processing system 400 comprises: a reaction chamber 410; a gas manifold 420; a fluorine precursor source 430A; a hydrogen precursor source 430B; an inert gas source 430C; a pathway 440 disposed between the gas manifold 420 and the reaction chamber 410; and a plurality of gas lines 450A-450C linking the gas sources 430A-430C with the gas manifold 420.

The reaction chamber 410 comprises a substrate holder 410A configured to hold a substrate to be processed; and a showerhead 410B for distributing the gas onto the substrate. The gas manifold 420 receives the gases from the different sources 430A-430C and mixes them prior to the gases entering the reaction chamber 410. The substrate holder 410A may have an ability to control its temperature among different parts of the substrate holder 410A.

In an exemplary process in accordance with at least one embodiment of the invention, a substrate may have both a silicon oxide film and a silicon nitride film deposited on it. The silicon nitride film may be a critical part of the integrated circuit or a mask layer to protect another layer on the patterned substrate. During processing steps, a top portion of the silicon nitride layer may be exposed to an ambient environment, converting a portion of the silicon nitride layer into a silicon oxynitride layer. Processes in accordance with at least one embodiment of the invention may be used to remove both the silicon oxide layer and the silicon oxynitride layer, but keep the silicon nitride layer intact.

The particular implementations shown and described are illustrative of the invention and its best mode and are not intended to otherwise limit the scope of the aspects and implementations in any way. Indeed, for the sake of brevity, conventional manufacturing, connection, preparation, and other functional aspects of the system may not be described in detail. Furthermore, the connecting lines shown in the various figures are intended to represent exemplary functional relationships and/or physical couplings between the various elements. Many alternative or additional functional relationship or physical connections may be present in the practical system, and/or may be absent in some embodiments.

It is to be understood that the configurations and/or approaches described herein are exemplary in nature, and that these specific embodiments or examples are not to be considered in a limiting sense, because numerous variations are possible. The specific routines or methods described herein may represent one or more of any number of processing strategies. Thus, the various acts illustrated may be performed in the sequence illustrated, in other sequences, or omitted in some cases.

The subject matter of the present disclosure includes all novel and nonobvious combinations and subcombinations of the various processes, systems, and configurations, and other features, functions, acts, and/or properties disclosed herein, as well as any and all equivalents thereof. 

The invention claimed is:
 1. A method for selectively etching a film disposed on a substrate, the method comprising: providing a substrate in a reaction chamber of a semiconductor processing device, wherein the substrate has an oxide layer, a nitride layer, and an oxynitride layer; performing a first etching process, wherein the first etching process comprises flowing a hydrogen precursor gas, a fluorine precursor gas, and an inert gas onto the substrate; performing a second etching process, wherein the second etching process comprises flowing a hydrogen precursor gas, a fluorine precursor gas, and an inert gas onto the substrate; wherein the first etching process is repeated a predetermined number of times and the first etching process removes the oxynitride layer from the substrate and keeps the nitride layer substantially intact; and wherein the second etching process is repeated a predetermined number of times and the second etching process removes the oxide layer from the substrate and keeps the nitride layer substantially intact.
 2. The method of claim 1, wherein the first etching process further comprises performing a bake step on the substrate, wherein the bake step has a temperature ranging between 50° C. and 400° C.
 3. The method of claim 1, wherein the second etching process further comprises performing a bake step on the substrate, wherein the bake step has a temperature ranging between 50° C. and 400° C.
 4. The method of claim 1, wherein the hydrogen precursor gas comprises at least one of: ammonia (NH₃); hydrazine (N₂H₄); or urea (NH₂CONH₂).
 5. The method of claim 1, wherein the fluorine precursor gas comprises at least one of: nitrogen trifluoride (NF₃); carbon tetrafluoride (CF₄); sulfur hexafluoride (SF₆); hydrogen fluoride (HF); hydrofluoric acid (HF) with water vapor; or fluorine (F₂).
 6. The method of claim 1, wherein the hydrogen precursor gas comprises at least one of: hydrogen (H₂); hydrogen fluoride (HF); hydrogen chloride (HCl); water (H₂O); an alcohol; an acidic gas or an acidic anhydride; or a mixture of any of the above.
 7. The method of claim 1, wherein the oxide layer comprises at least one of: silicon oxide; germanium oxide; aluminum oxide; cobalt oxide; or tungsten oxide.
 8. The method of claim 1, wherein the nitride layer comprises at least one of: silicon nitride or metal nitride.
 9. The method of claim 1, wherein the inert gas comprises at least one of: argon; krypton; helium; xenon; or nitrogen.
 10. The method of claim 1, wherein the first etching process has a duration ranging between 1 and 30 seconds.
 11. The method of claim 1, wherein the first etching process has a temperature ranging between −20° C. and 150° C.
 12. The method of claim 1, wherein the first etching process has a pressure ranging between 0.1 and 600 Torr.
 13. The method of claim 1, wherein the second etching process has a duration ranging between 5 and 120 seconds.
 14. The method of claim 1, wherein the second etching process has a temperature ranging between −20° C. and 150° C.
 15. The method of claim 1, wherein the second etching process has a pressure ranging between 0.1 and 600 Torr. 